I am trying to create a central bibliography (.bib file) in a directory outside of my LaTeX project. I want to do this so I don't have to have different .bib's for each paper I write. Currently in each .tex file I write:

\bibliography{central-bibliography}

at the end where I want to put it. My .bib file is called central-bibliography.bib.
The .bib file is in the same directory as the .tex file.

If I put the .bib file in an arbitrarily located directory, how would I reference it in the .tex file?

With a recent TeX Live, you can simply place your .bib file in the appropriate place and it will be found, so you can use

\bibliography{myfile}

with no path at all. With an older TeX Live you may need to run texhash first. MiKTeX also allows the same local installation procedure.

The only minor issue with placing a .bib file in your local texmf tree is that it's not so convenient for editing as if it were in the Documents folder. I get around this by using a link, so I actually have my .bib file on my Mac in ~/Documents/Literature and link from there to ~/Library/texmf/bibtex/bib/local using the Unix ln command. On Windows 7 you can do a similar thing using the mklink (you need to have Admin rights to do this).

An alternative approach is to use the BIBINPUTS environmental variable to set a path to be searched for .bib files, again allowing you use the file name directly with no path. Setting environmental variables depends on the operating system you are using.

TeX Live is slightly pickier about placement of these files. ".bib" files go in ~/Library/texmf/bibtex/bib or subfolders of this directory, and ".bst" files go in ~/Library/texmf/bibtex/bst or subfolders of this directory.
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AnsdMar 16 '14 at 12:52

I found a solution finally and it is work 100%. This is help you to creating central bibliography for all documents and also mendeley sync your library automaticly.

First you have to locate your main MikTex file directory and "base" file. Mine is

C:\Program Files (x86)\MiKTeX 2.9\bibtex\bib\base

If you use windows 7 or later you definitelly set mendeley for working admin at all time.
Right click on mendeley shortcut or .exe and select properties. In the Properties box, select the Compatibility tab and then check “Run this program as an administrator”. It is done.

Second you have to set mendeley for creating "library.bib" in this location. It is simple open mendeley and go

tools > options > bibtex

click browse and set it for "base" file location.

Refresh your library or close and open mendeley. Make sure library.bib file is created in